G7 & ink sequence

[tnflyer]

Attempting a G7 calibration on a press and having trouble with the overprint colors, (red, green, blue). Ink supplier suggests changing sequence to KCYM. I am skeptical. Thoughts? I would really like to hear if anyone has tried this & your experiences. Has anyone profiled with varying sequences?

 

[color_matters]

I have come across this blog by Gordon Pritchard hope it helps.

The Print Guide: Ink Sequence

 

[rich apollo]

Attempting a G7 calibration on a press and having trouble with the overprint colors, (red, green, blue). Ink supplier suggests changing sequence to KCYM. I am skeptical. Thoughts? I would really like to hear if anyone has tried this & your experiences. Has anyone profiled with varying sequences?

G7 is intended to run a KCMY ink sequence. I don't suppose there's any colorimetric reason you couldn't run the inks in another sequence, but I really don't think it's a good idea. You'll be increasing the risk of backtrap from M to Y, and you will distort your ink trapping.

What is the specific problem you're having?

 

[tnflyer]

G7 is intended to run a KCMY ink sequence. I don't suppose there's any colorimetric reason you couldn't run the inks in another sequence, but I really don't think it's a good idea. You'll be increasing the risk of backtrap from M to Y, and you will distort your ink trapping.

What is the specific problem you're having?

The problem seems to be magenta. I can get CYK to less than 1 Delta E. Magenta is always borderline. I can get blue & green overprints to 2 to 3 Delta E Adjusting densities sometimes brings red overprint close to tolerance, but still out, and gray overprint always out. Ink supplier says magenta & red will fall in if I change sequence to KCYM. My concern goes beyond solid ink LAB. What will happen to overall press gamut with a change in sequence? I could profile the press with different sequences, it might even be fun, however I would probably not have that much press time available (big surprise).

 

[gordo]

Along with the comments by Rich - a KCYM ink sequence will skew your color gamut and mean that you will have difficulty printing to an ISO/GRACoL 7 proof. Your greens will suffer, your blue/purples will be better, your reds will skew towards orange especially since yellow is usually the greatest area coverage in separations.

You need to talk to a different ink supplier.

best, gordo

 

[tmiller_iluvprinting]

You can measure a draw down of the magenta ink to see if it indeed is an ISO-12647 compliant ink. I f you can't find an ink film thickness from the draw down that gives you passing Lab numbers, then it won't matter what ink sequence you use. It is possible that your ink could fail right out of the can..
Regards,
Todd

 

[Bondi_dan]

Along with the comments by Rich - a KCYM ink sequence will skew your color gamut and mean that you will have difficulty printing to an ISO/GRACoL 7 proof. Your greens will suffer, your blue/purples will be better, your reds will skew towards orange especially since yellow is usually the greatest area coverage in separations.

best, gordo

ISO Standard 12647-2 Series specifies KCMY sequence. The G7 Methodology is in sync with 12647-2 and also recommends KCMY.

Regards,

 

[gordo]

@tnflyer

What solid densities are you running? (also status T or E?)
What are your overprint RGB trap values?
Which instrument are you using to measure the CIE L*a*b* values?
What formula are you using to calculate DeltaE?

best, gordo

 

[tnflyer]

@tnflyer

What solid densities are you running? (also status T or E?)
What are your overprint RGB trap values?
Which instrument are you using to measure the CIE L*a*b* values?
What formula are you using to calculate DeltaE?

best, gordo

Gordo,
lowest Delta E (76) values are at;
C-1.37
M-1.45
Y-1.02
K-1.58 status T
Using both X rite 530 & i1pro, there is a bit of difference in readings in the 2 instruments, but they are close. Using 530 at press & i1 with measure tool for the curve software.
I get that the ink supplier is trying to get me off their back, however, they don't seem to get that there is a concern beyond solid ink LAB, it does me no good to hit solid ink LAB numbers & then shift gamut. I'm mostly wondering how accurately can a shift be predicted (if at all) without actually re-arranging the sequence?

 

[gordo]

Gordo,
lowest Delta E (76) values are at;
C-1.37
M-1.45
Y-1.02
K-1.58 status T

I get that the ink supplier is trying to get me off their back, however, they don't seem to get that there is a concern beyond solid ink LAB, it does me no good to hit solid ink LAB numbers & then shift gamut. I'm mostly wondering how accurately can a shift be predicted (if at all) without actually re-arranging the sequence?

Your SIDs are where they should be.
What are your trap numbers?
What are the CIE LAB values of your CMYK and RGB solids?
What is the LAB value of your paper?

Just trying to confirm where the failure is occurring.

best, gordo

 

[tnflyer]

Your SIDs are where they should be.
What are your trap numbers?
What are the CIE LAB values of your CMYK and RGB solids?
What is the LAB value of your paper?

Just trying to confirm where the failure is occurring.

best, gordo

C=55.66 -36.97 -46.31
M=48.42 68.03 -5.34
Y=87.05 -2.66 87.19
K=16.59 -1.02 0.88
R=47.94 59.79 39.07
G=57.50 -50.82 32.49
B=28.17 20.86 -42.08
Paper=93.76 0 1.07
I'll have to get the sheets & measure trap again, didn't put that in my notes.
As I said earlier, magenta is a problem. Red & green way out, blue & 3 color barely in (threshold of 5 DE)
I can play around with magenta density & get it better, but usually pushes out elsewhere.

 

[tmiller_iluvprinting]

From the Lab numbers that you supplied I see 2 problems. The magenta and the yellow both fail(de>5). The magenta has a dE of 6.4, and the yellow has a dE of 6.6. Your paper fails also, but this isn't as important as your inks. Your magenta ink is broke, L* and a* are the priority for magenta, b* is what it is, but can go positive if you put too much ink down. The yellow you should be able to adjust the ink film thickness to swing the b* where it needs to be(characteristic of yellow ink-b* star moves quickly with density changes.)
regards,
Todd

 

[tnflyer]

From the Lab numbers that you supplied I see 2 problems. The magenta and the yellow both fail(de>5). The magenta has a dE of 6.4, and the yellow has a dE of 6.6. Your paper fails also, but this isn't as important as your inks. Your magenta ink is broke, L* and a* are the priority for magenta, b* is what it is, but can go positive if you put too much ink down. The yellow you should be able to adjust the ink film thickness to swing the b* where it needs to be(characteristic of yellow ink-b* star moves quickly with density changes.)
regards,
Todd

Should have mentioned also targeting SWOP3

 

[tmiller_iluvprinting]

If SWOP3 is your target, that makes your dE readings even worse......magenta dE=8.8, yellow dE=7.2. Your paper is worse also dE=4.3.
Regards,
Todd

 

[tnflyer]

If SWOP3 is your target, that makes your dE readings even worse......magenta dE=8.8, yellow dE=7.2. Your paper is worse also dE=4.3.
Regards,
Todd

Am I using wrong targets or measurements? I show SWOP3 yellow target of 88, -5, 88, which would give me a Delta E of 2.65, wouldn't it?

 

[rich apollo]

Take a look at the attached JPEG. I'm comparing your numbers (magenta triangles) to the SWOP3 targets (cyan dots) - pulled directly from the measurement data. Magenta is a little off-hue, but not terrible. To my eye, it looks there's a significant trapping problem on the yellow unit. I wonder if the unit isn't under-packed.

If you send me your P2P measurements, I can give you more feedback.

 

[tmiller_iluvprinting]

Am I using wrong targets or measurements? I show SWOP3 yellow target of 88, -5, 88, which would give me a Delta E of 2.65, wouldn't it?

My mistake-I was using the Lab numbers from ISO 12647-2:2004, and from the G7 How-To which is based on 12647-2:2004/Amd. 1:2007. I did not realize that the SWOP 3 and 5 aims were not the same. Sorry for causing confusion.
Regards,
Todd

 

[tmiller_iluvprinting]

@Rich,
Wouldn't it be more appropriate to use the target values for primaries and secondary overprints/traps as they are listed in the G7 How-To if one was doing a G7 calibration, and if one wanted to target the SWOP3 color space?
Regards,
Todd

 

[rich apollo]

@Rich,
Wouldn't it be more appropriate to use the target values for primaries and secondary overprints/traps as they are listed in the G7 How-To if one was doing a G7 calibration, and if one wanted to target the SWOP3 color space?

either way. These were just easier to find at the moment. The only difference is that the one's in the profile are a bit more precise.